A directional coupler includes first and second transmission lines, first and second coupling lines, a termination resistor, a coupling signal output terminal, and an impedance-adjusting circuit. The first coupling line is electromagnetically coupled to the first transmission line. The second coupling line is connected in series with the first coupling line and is electromagnetically coupled to the second transmission line. The termination resistor is connected to an end portion of the first coupling line that is on the opposite side from the end portion of the first coupling line that is connected to the second coupling line. The coupling signal output terminal is connected to an end portion of the second coupling line that is on the opposite side from the end portion of the second coupling line that is connected to the first coupling line. The impedance-adjusting circuit is connected between the first and second coupling lines.